1. Field of the Invention
The present invention relates to a polishing apparatus and a polishing method.
2. Description of the Related Art
Along with higher integration and multiple layer interconnection of semiconductor devices, flattening of various inter-layer insulation films or other films has become important in the process of production of a semiconductor device.
A variety of means have been proposed as a flattening technology. In recent years, attention has been paid to chemical mechanical polishing (CMP) using the mirror-like polishing technology of silicon wafers. Methods of flattening utilizing this are being developed.
An example of a polishing apparatus using a CMP process as a background of the present invention will be described with reference to FIG. 1.
A polishing apparatus 301 shown in FIG. 1 has a main shaft spindle 303 for rotating a polishing tool 302 and a table 304 for holding a wafer W.
The table 304 is rotatably mounted on a slider 306 provided to be able to move in an X-axial direction along a rail 305. It is driven to rotate by a rotation driving means constituted by for example a motor, a pulley, a belt, etc.
The main shaft spindle 303 is held to be movable in a Z-axial direction and is positioned at a target position in a Z-axial direction by a not illustrated drive mechanism.
In the polishing apparatus 301 having the above constitution, first, the wafer W is rotated at a predetermined speed. Slurry obtained by mixing a polishing abrasive such as silicon oxide into a liquid such as an aqueous solution of potassium hydroxide is fed as an abrasive from a not illustrated slurry feeder onto the wafer W.
Next, the polishing tool 302 is rotated at a predetermined speed, and the wafer W and the polishing tool 302 are positioned in the X-axial and Z-axial directions so that an outer circumferential edge of the polishing tool 302 overlaps and contacts the outer circumferential edge surface of the wafer W.
The polishing tool 302 is positioned in the Z-axial direction so as to obtain a predetermined depth of cut to the wafer W. Due to this, a predetermined polishing pressure is generated between the polishing tool 302 and the wafer W. In this state, the wafer W is moved in the X-axial direction with a predetermined speed pattern. The wafer W is polished while bringing the polishing tool 302 in contact with the wafer W, whereby the wafer W is flattened.
Summarizing the disadvantages, in the polishing apparatus 301 of the above configuration, the polishing surface 302a of the polishing tool 302 is parallel to the holding surface of the rotation table 304, and the overlapping regions of the polishing surface 302a of the polishing tool 302 and a surface to be polished of the wafer W contact each other over their entire surfaces according to the relative movement of the polishing tool to the wafer W 302 in the X-axial direction. For this reason, the area of the effective working region of the polishing surface 302a of the polishing tool 302 to the surface to be polished of the wafer W becomes a region where the polishing surface 302a of the polishing tool 302 and the surface to be polished of the wafer W overlap. This area is relatively large and varies according to the relative movement of the polishing tool 302 in the X-axial direction.
When the area of the effective working region of the polishing surface 302a of the polishing tool 302 to the surface to be polished of the wafer W is large, the amount of polishing in the effective working region is apt to be uneven due to the irregularities of the surface to be polished of the wafer W. If the area of the effective working region varies, the amount of polishing per unit time, that is, the polishing rate, varies, so it is difficult to uniformly polish the surface to be polished of the wafer W. Further, when the polishing surface 302a of the polishing tool 302 and the surface to be polished of the wafer W are parallel, the slurry cannot easily penetrate between the polishing surface 302a of the polishing tool 302 and the surface to be polished of the wafer W, so the amount of polishing again sometimes does not become stable.
For this reason, in the related art, for example, as shown in FIG. 2A, the polishing was performed by inclining a axis K1 of the polishing tool 302 toward the direction of advance of the polishing tool 302 by an inclination angle xcex1.
Here, FIG. 3 is a view of the distribution of pressure generated between the polishing surface 302 a of the polishing tool 302 and the surface to be polished of the wafer W when the axis K1 of the polishing tool 301 is inclined in the direction of advance of the movement of the polishing tool 302. Note that FIG. 3 shows the distribution of virtual pressure when polishing the surface to be polished of the wafer W by just rotating the polished tool 302 without rotating the wafer W.
As shown in FIG. 3, the distribution of the pressure generated between the polishing surface 302a of the polishing tool 302 and the surface to be polished of the wafer W becomes an approximately crescentic region PR. In this crescentic region PR, an area PH where the pressure is relatively high is generated inside and an area PL where the pressure existing around this is relatively low is generated. The area PH where the pressure is relatively high exhibits an approximately symmetric shape about the X-axis. This area PH becomes a region effectively acting upon the surface to be polished of the wafer W. The area PH is made sufficiently smaller than the overlapping area of the wafer W and the polishing surface 302a of the polishing tool 302. Even if the polishing tool 302 moves relatively in the X-axial direction, the surface area of the area PH becomes approximately constant. For this reason, the amount of polishing in the effective working region can be made uniform, and the polishing rate can be made constant.
However, the polishing tool 302 is for example an elastic member made of for example a disk-shaped member and formed by polyurethane foam or other plastic. It is pressed against the surface of the wafer W by a polishing pressure F as shown in FIG. 3. For this reason, the polishing tool 302 pressed against the wafer W resiliently deforms.
In addition, if the polishing surface 302a of the polishing tool 302 is inclined to the wafer W surface by the inclination angle xcex1, the polishing surface 302a of the polishing tool 302 deforms in a riding region 190 and a relief region 191 shown in FIG. 3 as shown in for example FIGS. 4A and 4B when riding up on the wafer W. In the riding region 190, as shown in FIG. 4A, the polishing surface 302a of the polishing tool 302 rides up on the surface of the wafer W from an outer circumferential edge EG of the wafer W, so the polishing surface 302a of the polishing tool 302 resiliently deforms and the polishing surface 302a immediately before the riding up on the surface of the wafer W located in the vicinity of the outer circumferential edge EG protrudes downward from the surface of the wafer W. In the relief region 191, as shown in FIG. 4B, the polishing surface 302a of the polishing tool 302 passes the outer circumferential edge EG from the top of the surface of the wafer W and then separates from it, so the resiliently deformed polishing surface 302a of the polishing tool 302 separates from the outer circumferential edge EG of the wafer W and the deformation is restored while the stress is eased.
When the polishing surface 302a of the polishing tool 302 resiliently deforms, the portion of the polishing surface 302a protruding downward from the surface of the wafer W strongly contacts the outer circumferential edge EG of the wafer W, the majority of the working energy is consumed for the work of the protruding portion of the polishing surface 302a riding up on the outer circumferential edge EG of the wafer W, and, as shown in FIG. 3, damage DM is given to the outer circumferential edge of the wafer W.
When damage to the outer circumferential edge EG of the wafer W due to the protruding portion of the polishing surface 302a accumulates, since the wafer W is rotating, for example, as shown in FIG. 5, an excessively polished portion 402a is formed at the entire area of the outer circumferential portion of the wafer W. When the excessively polished portion 402 is formed, there is the disadvantage that the number of semiconductor chips formed on a wafer W and able to be taken becomes small, so the yield is lowered.
The amount of the wafer W surface polished away per unit time, that is, the polishing rate, is lowered by the amount of the working energy consumed for the excessive polishing of the outer circumferential edge EG of the wafer W, the number of wafers W polished per unit time is lowered, and therefore the productivity is lowered.
In the region where the polishing surface 302a of the polishing tool 302 rides up on the outer circumferential edge EG of the wafer W, the slurry cannot easily penetrate between the polishing surface 302a and the surface of the wafer W, so the slurry fed between the polishing surface 302a and the wafer W becomes insufficient and therefore the polishing rate is lowered. In order to make up for the shortage of slurry, a large amount of expensive slurry must be fed, so the productivity is lowered.
In the region where the polishing surface 302a of the polishing tool 302 rides up on the outer circumferential edge EG of the wafer W, the damage to the polishing surface 302a is also large, the quality of the polishing surface 302a is apt to abruptly deteriorate, and therefore fluctuation of the polishing conditions easily occurs. In order to prevent the fluctuation of the polishing conditions, it is necessary to condition the polishing surface 302a by a means such as dressing. If the frequency of the conditioning for achieving a suitable state of the polishing surface 302a increases, the productivity of the polishing apparatus is lowered.
An object of the present invention is to provide a polishing apparatus and a polishing method capable of suppressing excessive polishing of the outer circumferential edge of a surface to be polished of a polished object due to elastic deformation of the polishing tool and capable of stabilizing the polishing rate.
According to a first aspect of the present invention, there is provided a polishing method for rotating a polishing tool formed by an elastic member having a polishing surface along a plane perpendicular to a rotary shaft, pressing the polishing surface to a surface to be polished of an object to be polished held on a holding table, and relatively moving the object to be polished and the polishing tool along a holding surface of the holding table, to polish the surface of the object to be polished, said method comprising the steps of: inclining the rotary shaft of the polishing tool by a predetermined angle to a direction perpendicular to the holding surface of the holding table and toward a direction of advance of the movement of the polishing tool, and inclining the shaft of the polishing tool to the direction perpendicular to the holding surface of the holding table and in a direction reducing elastic deformation of the polishing surface in a region where the polishing surface rides up on an edge of the surface.
The polishing is carried out by interposing an abrasive between the polishing surface and the surface to be polished.
Preferably, the shaft is inclined along a plane perpendicular to the direction of advance of the movement of the polishing tool to reduce the elastic deformation of the polishing surface.
Further, preferably, the shaft is inclined in a direction where the height of the polishing surface with respect to the surface to be polished in the region of the polishing surface riding up on the outer circumferential edge of the surface to be polished becomes higher than the height of the polishing surface in a region of the surface to be polished away from the surface to be polished.
Preferably, the polishing is carried out by using a polishing tool having an annular polishing surface.
Use is made of a polishing tool having a polishing surface faced by making the polishing tool rotating in a state with the shaft inclined in different directions relatively move along a correction surface of a correction tool parallel to the holding surface.
According to a second aspect of the present invention, there is provided a polishing method for rotating a polishing tool formed by an elastic member having a polishing surface along a plane perpendicular to a rotary shaft, pressing the polishing surface to a surface to be polished of an object to be polished held on a holding table, and relatively moving the object to be polished and the polishing tool along a holding surface of the holding table, to polish the surface of the object to be polished, said method comprising the steps of: inclining the shaft of the polishing tool to the direction perpendicular to the holding surface of the holding table and in a direction reducing elastic deformation of the polishing surface in a region where the polishing surface rides up on an edge of the polished surface.
According to a third aspect of the present invention, there is provided a polishing apparatus comprising: a holding table for holding an object to be polished, a polishing tool having a polishing surface vertical to a rotatable shaft, a polishing tool holding means for holding the polishing tool rotatably about the shaft, a moving and positioning means for holding the polishing tool holding means in a direction where the polishing surface of the polishing tool faces the surface of the object and determining a relative position of the polishing surface to the surface in the facing direction, and a relative moving means for relatively moving the polishing tool and the object on the holding table along the holding surface of the holding table, wherein the rotary shaft of the polishing tool is inclined at a predetermined angle in a direction from a direction perpendicular to the holding surface of the holding table toward the direction of advance of the movement of the polishing tool and is inclined by a predetermined angle in a direction different from that inclination direction and reducing the elastic deformation of the polishing surface in the region where the polishing surface rides up on the outer circumferential edge of the surface to be polished.
In the present invention, since the polishing is carried out by inclining the polishing tool in a direction reducing the elastic deformation of the polishing surface in the region where the polishing surface rides up on the outer circumferential edge of the surface to be polished of the object to be polished, the damage exerted upon the outer circumferential edge of the surface to be polished due to the elastic deformation by the polishing surface riding up on the outer circumferential edge of the surface to be polished is suppressed, so concentration of a working energy of the polishing surface at the outer circumferential edge of the surface to be polished is suppressed. As a result, the reduction of the polishing rate is suppressed.
Further, by inclining the polishing surface to the surface to be polished, the height of the polishing surface to the surface to be polished in the riding region becomes relatively high, therefore when the abrasive to be interposed between the polishing surface and the surface to be polished is fed, the abrasive can easily penetrate between the polishing surface and the surface to be polished in the riding region toward the rotation direction of the polishing surface, so a sufficient amount of the abrasive is stably fed between the polishing surface and the surface to be polished.
Further, by inclining the shaft of the polishing tool to a direction vertical to the holding surface of the holding table by a predetermined angle toward the direction of advance of the polishing tool, the effective contact area of the polishing surface and the surface to be polished is made narrower. Due to this, unevenness of the distribution of the amount of polishing of the surface to be polished in the contact area is suppressed and variation of the amount of polishing in the surface to be polished is suppressed. On the other hand, when the rotary shaft of the polishing tool is inclined by a predetermined angle to a direction perpendicular to the holding surface of the holding table toward the direction of advance of the movement of the polishing tool, at the forward portion of the polishing surface in the direction of advance of the movement of the polishing tool, a larger elastic deformation occurs in the region riding up on the surface to be polished than a case where there is no inclination and the damage exerted upon the outer circumferential edge of the surface to be polished will increase, but in the present invention, the shaft of the polishing tool is inclined in a direction of reducing the elastic deformation in the riding region of the polishing surface, so the damage exerted upon the outer circumferential edge of the surface to be polished can be suppressed.
Further, in the present invention, by polishing using the polishing tool with the polishing surface inclined to the plane perpendicular to the shaft at approximately the same angle as the inclination angle toward the direction of advance of the movement of the polishing tool, the polishing surface becomes a curved surface, the effective contact area of the polishing surface and the surface to be polished is made narrower, and the height of the polishing surface to the surface to be polished in the region riding up on the surface to be polished becomes high, the amount of elastic deformation of the polishing surface is further reduced and the damage exerted upon the outer circumferential edge of the surface to be polished due to the elastic deformation of the polishing surface can be further suppressed.